1. Technical Field of the Invention
This application is based on applications Nos. 9-113804, 9-118177, 9-118178, and 10-69667, filed in Japan, the contents of which are hereby incorporated by reference.
The present invention relates to a driving mechanism, and particularly to a driving mechanism which utilizes changes in the shape of a shape-memory alloy for various mechanical actions.
2. Description of Related Art
There are many different kinds of mechanical actions, and driving mechanisms for these actions are respectively designed in accordance with different purposes. However, while various appliances are desired to be multifunctional and high speed, demands which are contradictory to each other and thus difficult to accomplish, such as minimization, higher precision, quietness of the actions, have been increased. Taking cameras as the example, some of the conventional driving mechanisms as well as their problems will be hereinafter described.
A built-in pop-up flash of a camera is constructed as shown in FIG. 1, in which a flash 102 is urged upwardly by a spring 104 but is normally retained in a housed position (initial position) by a lever 111 against the force of the spring 104. The lever 111 is urged by a spring 113 to remain in a locking position, and when the lever 111 is released from this state, the flash 102 is popped up by the force of the spring 104. Such release is made either manually with an operative member or automatically in accordance with automatic measurement of light.
FIG. 2 shows a sequence of actions in the flash pop-up mode in which the case using a plunger 113 shown in FIG. 1 is taken as an example. First, an electric current is applied to the electromagnetic plunger 117, by which the lever 111 releases a hold of the flash 102, which is freed and popped up by the urging force of the spring 104 from the housed position shown in FIG. 1A to a state shown in FIG. 1B. At the same time a switch 119 is turned off, and the application of the electric current to the electromagnetic plunger 117 is ended by this switch-off signal, whereby the camera is set to a standby mode. When the electricity to the electromagnetic plunger 117 is shut off, the lever 111 is freed and returned to the locking position by the urging force of the spring 113 as shown in FIG. 1C so as to prepare for the next locking action when the flash 102 is housed again. In this example, the flash 102 is housed by pushing it in by a hand.
In such a construction, however, the camera cannot be further minimized in dimensions since the plunger has a large volume and needs to be disposed on an upper part of the camera. It is possible to provide a motor instead of the plunger to allow the lock of the flash to be released by a rotational force of the motor. However, such provision of the motor specially for the lock releasing action would be also disadvantageous for minimization of the camera. The necessity of providing an additional motor may be obviated by using a part of rotation of a motor for charging shutter, but in that case it will be further necessary to provide a linking mechanism and a drive force switchover mechanism and the like between the two, leading to an increase in number of components as well as causing the structure to be complicated, thus ending up to be disadvantageous for minimization of the mechanism and reduction of cost.
A second example of driving mechanism is designed for a film feeding system and a zooming system of cameras, which are driven by a drive force switched over from a single motor and transmitted to either of them depending on needs. Such driving mechanism allows a multifunctional camera to have fewer number of motors.
In the zooming system, a lens tube is driven tele- and wide-scopically, instantly responding to operations by a user.
In the film feeding system, for example, in the case of an advanced photo system camera, since the film is pushed out from a cartridge or rewound into the cartridge, a fork shaft which is engaged with a cartridge spool needs to be rotated in both regular and reverse directions. A take-up spool inside the camera also needs to be rotated in a film take-up direction for a so-called thrust drive when the fork is rotated in a direction to push out the film from the cartridge. For satisfying these demands, rewinding of the film is achieved by the rotation of the motor in one direction, and the thrust drive and spool take-up drive are achieved by the rotation in the reverse direction in an ordinary mechanism.
In such a case, it is necessary to switch over the rotation of the motor in normal and reverse directions to the zooming system and the film feeding system. A switchover means which the applicant of the present invention has previously proposed as disclosed in Japanese Published Unexamined Patent Application No. 1-287648 employs a friction planet gear mechanism. As the transmission is changed over from one to another by the rotation of motor in either one of directions in this mechanism, it is necessary to lock the planet gear so as to prevent the transmission from being changed over when transmitting a drive force and to release the lock of the planet gear when changeover of transmission is required. Such locking and releasing may be achieved using actions of an electromagnetic plunger. However, as a plunger takes up a lot of space, its usage is limited within a compact camera. Also, it is necessary to supply electricity to two loads at the same time since the changeover of the planet gear is performed such that an electric current is applied to the motor while electricity is also applied to the plunger. This increases the load on a battery, and the capacity of motor will have to be reduced, which will result in decrease in driving speed.
For focusing lenses in cameras, it is required to move a focusing lens to a predetermined position and stop it there in accordance with the distance to an object to be photographed. Also, for driving a zooming action of a flash, it is required to move a reflector umbrella to a prescribed position and stop it there in accordance with a zooming action of a photographing lens. Each are generally driven by a motor which is supplied with electricity from a battery. The motor is electrically controlled according to position detecting signals from a position detector which judges whether a driven member is located at the prescribed position, whereby the driven member is moved to a desired position and stopped there.
However, the motor has a large volume and requires a gear or the like for transmitting the rotation thereof to the driven member, and may further require a motion converting mechanism for converting rotation into a linear movement in case the movement of the driven member is reciprocating motion of one dimension. It is possible to employ another driving mechanism cooperatively with the motor to avoid increase in volume, in which case the construction will be any way complicated because a drive switchover mechanism and a transmission mechanism are necessary.
Further, when a motor or a gear is employed, since motors emit vibration sounds and gears emit noises generated by toothed gears meshing with each other, they are unsuitable for use under a quiet circumstance. Also, in the case of using gears, position control of the driven member will be more difficult due to backlash that is specific to a gear transmission system. It is especially disadvantageous for driving reciprocating motions such as when zooming tele- or wide-scopically.
These problems are not limited to cameras but commonly found in other driving mechanisms under similar circumstances for various purposes.
In view of the foregoing, it is a primary object of the present invention to provide a driving mechanism which is capable of favorable drive in accordance with various demands as described above utilizing a shape change stroke of a shape-memory alloy back to its memorized shape.
The above said object is addressed by one aspect of the present invention which provides a novel driving mechanism including a driven member biased toward one direction from an initial position, a locking mechanism for retaining the driven member at the initial position against a biasing force, a shape-memory alloy of which transformation into a memorized shape by electric heating is used for lock release operation for releasing the lock by the locking mechanism, and a controller by which electric heating of the shape-memory alloy for releasing the lock is completed after a predetermined period of time has passed since the start of electricity supply.
To accomplish the said object, a driving mechanism for driving a plurality of driven members selectively according to another aspect of the present invention comprises a first driving power source which is a motor, a second driving power source which is a shape-memory alloy, a transmission changeover mechanism for selectively transmitting a drive force from the first driving power source to a specific one of the plurality of driven members, wherein the transmission changeover mechanism performs a transmission changeover action by utilizing a shape change of the second driving power source.
A driving mechanism according to yet another aspect of the present invention comprises a driven member, a shape-memory alloy having a predetermined memorized shape, a driver for driving the driven member utilizing transformation of the shape-memory alloy, a sensor for detecting displacement of the driven member, and a controller for controlling the driver based on data from the sensor which detects displacement of the driven member.
Other and further objects, features and advantages of the invention will appear more fully from the following description.